JPS61100470A - Ink jet printer functioning as droplet discharge-distance compensation in combination - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention This invention relates to continuous flow page width inkjet printing, and is a means of correcting ink drop trajectories that sometimes cause changes in droplet distance and improving titration surface accuracy. The present invention relates to an inkjet printer equipped with.

BACKGROUND OF THE INVENTION As is well known in the art, inkjet printing is non-impact printing in which ink droplets are impinged onto a recording medium, such as paper. Inkjet printing is a big, drop-on-demand
) type and continuous flow type. In drop-on-demand, ink drops are ejected by a drop generator only when ink drops are needed to produce information on the recording medium. Continuous flow systems emit a continuous stream of ink droplets. Droplets not needed to print information on the recording medium are directed into a drainage channel where unused drops are collected and reused.

Continuous flow inkjet printers come in two basic configurations. One includes a drop generator with one or more nozzles that move back and forth across the recording medium. The other basic configuration has a fixed array of nozzles, each nozzle directing an ink droplet only to a selected portion of the recording medium on which it travels.

In continuous flow pagewidth printing, a linear array of stationary nozzles are arranged transversely to the direction of a moving recording medium, with each nozzle directing a stream of ink toward the recording medium. The ink from the nozzle is under a predetermined pressure and perturbed at a predetermined frequency so that the flow breaks into droplets at a fixed distance from the nozzle and continues to move at the same speed. Each nozzle is assigned the responsibility of printing a linear section, the entire linear section producing a line across the width of the recording medium. To spread the ink droplets of each nozzle over its section, each droplet is charged 1! at the point of ink stream ejection according to a digitized data signal. charged by the pole, this band 1
A drop is forced to pass through an electric field.

Unprinted ink drops go to the drain where they are collected for reuse and recycled to the ink supply.

Each of the multiple inkjet nozzles in a continuous flow print-through-page configuration fires ink drops to a predetermined location along its corresponding linear segment. If such an inkjet printer is functioning properly, ink drops from adjacent nozzles directed to opposite end positions of adjacent linear segments will not cause undesirable overlap or excessive gaps between them. Further details regarding this fffi inkjet printer, which are "stitched" together such that no
Obtained from No. 04.

After the ink drops from each nozzle are generated, they are deflected along each trajectory to a predetermined position within an assigned linear segment, so that the drop generator, charging electrode, etc. It is necessary to monitor and correct the performance of the components of the inkjet printer, such as the polarization field and the deflection field. 1
One important calibration check is checking the seam points between linear segments printed by ink drops from adjacent nozzles. If the inkjet printed image is not to be interrupted across the strike of the recording medium, neither drop overlap nor gaps between the flocculent sections are allowed.
From U.S. Pat. It is well known. This in-information monitors and corrects the charge to be applied to the next drop from each nozzle, accurately directing the drop to be printed to a designated impact or pixel location on the recording medium.

Research Disclosure No. 20123, January 1981, by S. C. Paranjpe, discloses a correction method for misdirected drops caused, for example, by manufacturing defects and dimensional tolerance variations.

Printing errors are now corrected by adjusting the charge voltage before placing the drop under the deflection field. The correction algorithm for each inkjet run can be evolved, and if desired, the correction algorithm can be changed over the life of the printhead as the jet misalignment caused by the printhead changes over time.

18M Technology Disclosure Bulletin (Te
Chnical Disclosure Bullet
in ), Vol, 22 s 7. 1979 12
The moon compensates for the flight time of a droplet from a reciprocating inkjet printhead to a fixed but step-movable recording medium, and during the droplet flight time from the printhead to the recording medium, Discloses a method for compensating for errors in impact position caused by movement.

M.II.? U.S. Patent No. 4.13 of Jevi11e et al.
No. 6.345 discloses several height sensing methods that detect a one-degree deviation in the height of a vertically extended drop train from a predetermined flight path and correct for that deviation in subsequent drops. . In one, drop velocity is determined and adjusted to the desired flight path by increasing or decreasing nozzle pressure.

U.S. Pat. No. 4,158,204 to L. Kuhn et al. discloses a scheme for compensating for velocity variations between multiple inkjet streams caused by causes such as nozzle defects, clearance, accumulation, ink build-up, etc. Velocity compensation between drop streams can be achieved by adjusting the time that the informative signal is applied to each drop charging electrode.

J.A., McDonnell et al., U.S. Pat. No. 3,86
No. 4.692 controls the flight path of an ink drop by varying the time that a voltage is applied to the deflection electrode, and applies a separate charge to each drop in the drop train according to the time that each drop is under the action of the deflection field. A method for providing different trajectories is disclosed.

R.S. Heard et al. U.S. Pat. No. 4.138.68
No. 8 discloses a method for controlling the flight path of ink droplets.

To compensate for errors in the drop arrangement caused by movement of the printhead relative to the recording medium, a voltage gradient is applied across at least one deflection electrode to induce a distortion of the electric field to compensate for drop misalignment caused by movement of the printhead. Compensate alignment. The amount of electric field distortion is controlled by automatically feeding and puffing a signal to a circuit that monitors the speed of the printhead and controls the electric field distortion between the deflection electrodes.

All of the above-mentioned conventional technologies are designed to recognize or aim at the problem of stitching point errors caused by changes in droplet ejection distance from the nozzle juxtaposed position to the recording medium in multi-nozzle page width printers. This is caused by, for example, changes in the thickness of the recording medium, slight curvatures or wrinkles in the recording medium, and changes in droplet ejection distance caused by tolerances of the recording medium support or platen.

(Object of the Invention) - An object of the invention is to improve the accuracy of titration onto a moving recording medium by a multi-nozzle, continuous flow inkjet printer.

Another object of this invention is to reduce the droplet ejection distance (i.e. from the inkjet printer nozzle to the recording medium surface).

The objective is to achieve improved drop device accuracy by generating a signal representative of the drop distance that is used to monitor the drop distance (distance) and adjust the drop trajectory as necessary.

Still another object of the present invention is to constantly monitor, for each nozzle or for each nozzle group, the droplet ejection distance to an adjacent linear section that crosses the hit of a recording medium that is continuously moving in a direction intersecting the movement of the recording medium. , consists in adjusting the trajectory of the drops emitted from one or more fixed nozzles assigned to each linear segment and compensating for positioning errors due to changes in droplet distance.

(Structure of the Invention) In one embodiment of the present invention, an optical distance sensing device is used to direct a light beam toward a recording medium and receive reflections therefrom to generate a signal proportional to the distance from the optical device to the recording medium. .

This signal is used to vary the deflection voltage of the deflection electrode or the gain of a charging amplifier connected to the charging electrode. This change in deflection or charging voltage adjusts the drop trajectory and moves the pixel or impact location in response to changes in droplet distance, resulting in drop volume spacing, particularly between adjacent pixel targets from separate adjacent nozzles. spacing is maintained accurately.

A fixed array of optical distance sensing devices is positioned parallel to and below the array of fixed nozzles at a predetermined distance from the recording medium. Each optical path '4 sensing device is assigned to a particular point or portion of the moving recording medium. Alternatively, optical distance sensing devices are mounted on vibrating bars, each device being placed parallel to a fixed nozzle. Since the movement of the vibrating bar is parallel to the nozzle and perpendicular to the direction of movement of the recording medium, one or more positions across the hitting area of the recording medium are scanned, and multiple droplet ejection distances due to wrinkles etc. of the recording medium are scanned. You can change the pick amp.

In another embodiment of the invention, a pneumatic proximity sensing device is used instead of the optical device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings and in particular to the first tooth, there is shown a schematic diagram of a continuous flow inkjet printer 10 that includes a jet column or manifold 13 that includes a plurality of nozzles or orifices 15 that emit an ink stream 14. A stationary inkjet generator 12 is provided. Although FIG. 1 is a side view and only one ink stream is visible, a linear array of nozzles 15 extends along the manifold and an ink reservoir 16 has a generator 12 that produces a series of parallel ink streams. The ink is then pumped into the generator 12 by a pump 18. The generator 12 includes a pump 18 that maintains the ink in the manifold 13 at a stable pressure sufficient to cause the ink to be ejected through the nozzles toward a recording medium moving in a direction perpendicular to the linear array of nozzles. An excitation m, z2, such as a piezoelectric device, is also coupled, which causes the ink stream 14 to break up into ink drops 24 at a predetermined distance from the nozzle. As the ink stream is broken into individual ink drops, charging electrode 26 induces a net charge on each drop according to a scheme or algorithm for the desired next drop trajectory.

Obi I! Downstream of the electrode 26 are a number of field generating or deflecting electrodes 2.
8 are located and these deflection electrodes are energized to the voltage necessary to create an electric field through which the charged droplets 24 must pass.As is well known, charged particles passing through an electric field
The particle experiences a force that depends on the magnitude and polarity of the charge on it and the strength of the electric field through which it passes. Therefore, the uncharged droplet passes through the deflection electrode 28 and heads toward the recording medium 20 without being affected by any shadow.

::/ 7Ej: Ura depends on the size and polarity of its charge,
deflected from its initial trajectory. 8 When a drop is formed and passes through a charging electrode, it carries an appropriate charging potential? By application to the f-electrode 26, the 8-electrode is directed to a desired impact location (hereinafter referred to as a pixel) or exhaust temperature 30 on the surface of the recording medium.

Continuous flow printer ink droplets have one polarity (monopolar system)
Or, it is known that charging can be performed with both polarities (bipolar method). FIG. 2 shows a bipolar system in which highly charged drops are directed to the exhaust lA>30 for circulation into the ink reservoir 16.

Droplets that are either uncharged or charged to such a level that trajectory 29 (indicated by the dotted line) does not reach discharge 30 are
The distance detection sensor that passes through the calibration monitor sensor 32 and the distance detection sensor 34 to the recording medium 20 will be described in detail later. Calibration monitor sensor 32 detects the path of ink drop 24 toward the recording medium and adjusts printer operation to
Ink from multiple ink streams? W are properly "stitched" together so that each incremental section "L" on the surface of the recording medium can be accessed or printed by a nozzle m assigned to that section. - with “
"Stitching" means that the centers of adjacent pixels from adjacent section "L" (see Figure 2) are located one pixel diameter apart, or a distance of the post-impact drop diameter (approximately 75 microns), and these pixels When printed, this means that they do not overlap too much or produce appreciable gaps between adjacent ones (total system tolerance for overlap or gaps is about 75 microns).

An example of a typical calibration sensor 32 use and application is the Cre
An et al., U.S. Pat. Included here as materials,
The function of the calibration sensor 32 is to calibrate the inkjet printer 10 by observing drops passing therethrough during a calibration mode of operation.

One application particularly suited to the present invention is where the second wandering groove 31 for ink drop circulation is used to thicken drops generated while calibrating the system by the calibration sensor 32. A high-speed inkjet device in which a continuous sheet of recording medium 20, such as paper, is moved past an ink drop generator 12 in a direction perpendicular to the nozzle array 15, as shown by arrow 17, where the paper is encoded with information. be done. Experience has shown that it is desirable to periodically recalibrate the printer to ensure that the ink drops 24 are directed to the desired areas or pixels on the recording medium 20. To perform this calibration, an ink drop is generated when the recording medium is not in a position to receive an ink drop;
Flight past the sensor 32: Calibration can be carried out, for example, between individual sheets of recording medium and when the movement of the recording medium is temporarily interrupted.

Therefore, a second discharge is necessary at each stitching point "P" (see Figure 2), i.e., when the recording medium is not in a position to receive an ink drop, a long and narrow discharge across the strike of the recording medium is required. It should be obvious that you should use

Any known recording media transport mechanism 36 transports each sheet of recording media at a controlled speed across the stream of ink droplets 24 emitted from the inkjet generator 12. Since the printer 10 is a high-speed device, unmarked sheets of recording media such as paper are sent to the conveyance mechanism 36, and the printer 10
A mechanism (not shown) must be included in the transport mechanism 36 for peeling off the recording medium from the transport mechanism after being encoded with the ink.

The method of continuous flow inkjet printing begins by receiving at controller input 50 a series of signals representing digitized or video data information. controller 3
8 converts these signals into digitized voltage representations which are output to a digital-to-analog converter 42 where the digital signal representing the new voltage is converted to an analog signal and applied to a power amplifier 52 . In addition to generating charging voltages for the plurality of charging electrodes 26, the controller 38 also controls the printer 1.
Monitor and/or provide control signals for various other components within 0. That is, as shown in FIG. 1, the controller 38 includes an amplifier 39 and an analog/digital converter 43
receives human power from the sensor 32 via the sensor 32 and controls the moving speed of the recording medium 20 via another amplifier 47 that drives the motor 45 and the second digital/analog converter 44;
a fourth digital-to-analog converter 41 and an amplifier 46 to control perturbations in the droplet generator 12 by the excitation source 22;
controls the pressure maintained in generator manifold 13 by pump 18 via. Although these functions are important for the operation of the inkjet printer 10, they are not directly related to the later-described feature of the present invention of correcting the droplet ejection distance for each nozzle or nozzle group, so they will not be explained in further detail here. .

The partial plan view of FIG. 2 shows several nozzles 15 containing a continuous ink stream 14, a charging electrode 26, a deflection electrode 28, a printing surface 19
, and each section “L′” assigned to a nozzle on the printing surface 19
It shows a sequentially unfolded or swept trajectory 29 printing . The recording medium 20 is indicated by a dotted line, showing a normal stitching point "P" on the printing surface, and approaching (+Z) and moving away from (-Z) the nozzle with respect to the normal stitching point, respectively.
The stitching points 1N'' and ``M'' are also shown for comparison.As a convenient direction reference, set the orthogonal coordinate system of x, y, z as shown in Figure 2.In other words, from the nozzle to the print surface The distance k towards 19 is the Z direction, and the direction in which the drops to be printed are spread out to print the section is the X direction.

Further, the +Y direction is the direction of movement of the recording medium (see arrow 17 in FIG. 1).

As mentioned above, a seam point is a boundary position between adjacent sections "L" printed by adjacent nozzles. A seam point is thus defined as a boundary between two end pixels that are included in separate adjacent segments and that touch or oppose each other. These two pixels are always printed by drops from separate but adjacent nozzles. Also, the centers of each of the two end pixels are at a distance equal to the diameter of the spot produced by the infiltration of the pixel, i.e. the recording medium Ui.
55 microfron ±) apart. By maintaining this relationship between the ink drops, especially at the seam points,
The drops produce high quality printing of information without excessive overlap or too much clipping.

As used here, the ink drop 24 is X-Zlm
They fly parallel to each other and all head toward pixels on the X-Y printing surface 19.

Printing is performed in a raster or swept pattern of scanned or printed lines of pixels, each nozzle being assigned a linear row of pixels forming a segment.

When all segments across the recording medium 20 are printed, a solid line is generated across the hit of the moving recording medium. One ink drop is directed to one particular pixel location within the assigned partition. The role of the sensor 32 is to ensure accurate placement of the drops relative to the pixels within the printing surface 19. That is, any errors in the drip device detected by sensor 32 can be corrected.

As mentioned above, a scanning or printed line of ink drops is deposited onto a target pixel along the X-axis direction, while the recording medium moves along the Y-axis direction. This relative movement
A two-dimensional Lasque image is produced consisting of a plurality of parallel printed lines of pixels, each printed line consisting of a section containing a predetermined number of pixels. The presence or absence of a droplet printed at each pixel is the vehicle by which an image of information is constructed.

In the printer 10, as shown in Figure 1.2, a stitched array of continuous streams of drops is opened in the
9 to form sections abutting each other end-to-end. These abutting ends are the above-mentioned stitching points P. Ink drops from adjacent nozzles printing two separate sections of abutting pixels are generally at a 6 degree printing surface 19
Each approaches the target pixel at an angle α relative to the target pixel.

Therefore, if a portion of the surface of the recording medium is not in alignment with the printing surface, as shown at locations M and N, the seam point will have an error of about 1 mil for every 5 mil change in the surface of the recording medium. At position N on the recording medium surface, the drops printing stitching points are too far apart from each other to form a gear knob, while at position M the drops overlap. For high quality printing 1), the total error allowed in the drop device is 0.3 mil. Generally, variations in paper thickness, variations in concentricity and roundness of the rolls along the transport mechanism 360 roller axis, and other cumulative tolerances and mechanical effects will result in a deviation of approximately 20 mils from the surface of the recording medium. occurs. The calibration sensor 32 cannot take into account such deviations in droplet distance, referred to as the printer's depth of focus. This is because the calibration algorithm performs the stitching based on the measurements obtained by the sensor 32 and extrapolates a hypothetical recording medium surface, here of course the printing surface 19.

The distance detection sensor 34 consists of an array of optical devices 48 or pneumatic proximity detection devices 49, and monitors the actual distance from each device force to a selected area of a certain object and compares it with the standard dimension. . Optical and pneumatic devices, or a combination of both, can detect the actual recording medium surface area to be printed, correct the drop trajectory, and control the drop placement and stitching by the controller 38, control circuit 27, intensifier 33 and Analog/digital converter 3
5 to within 0.3 mil tolerance.

The control circuit 27 has a light source for the optical device 48 and/or a pneumatic source for the pneumatic proximity device 49 . In either device, a signal is emitted from the sensor 34 representing the actual distance to the surface of the recording medium. This signal is received by control circuit 27 where it is compared with a signal representative of the distance from sensor 34 to printing surface 19. The results of this comparison are sent to the controller 38, which deflects the voltage applied to the charging electrode 26 or deflection electrode 28 and adjusts the trajectory of the next ejected drop.
Used to compensate for changes in droplet distance. The controller adjusts the trajectory of the droplet directed to each pixel on the recording medium located between the areas of the recording medium 20 actually detected by any two or more optical or pneumatic devices of the distance detection sensor 34 by two rounds. Use extrapolation to do this. This is feedforward control, or predictive control, since the actual image forming performance is not detected. The accuracy of the correction depends on the distance F,1 (the open loop gain of the sensing sensor 34, the deflection control circuit and the mechanical integrity of the drop generator 12).

Light path! If a detection sensor 48 is used, the sensor 48 typically includes a light emitter and a light receiver that receives reflected light from the actual printing surface. The reflected signal is incorrect in the distance from the optical device to the light scattering surface of the recording medium 20. An example of such an optical distance sensing device is the 11ewlett Packard
It is commercially available as HEDlooO from the company. H-ED
The IOQO has an integrated light emitting diode (LED) and a photodiode with a focusing lens. This device also includes an array of these light shields 48, which have 1111 fields at a distance of 4 degrees from the recording medium, mounted on a support structure 51. In one embodiment, support structure 51 is fixed, while in another embodiment, support structure 51 is
As shown by an arrow 53, it can be translated left and right by a predetermined distance along a direction parallel to the printing surface and perpendicular to the direction of movement of the recording medium. If movable, the optical device can detect droplet drop distance from the nozzle to at least two separate locations on the surface of the recording medium. Each optical device can correct the droplet ejection distance for each nozzle or for each group of multiple nozzles.

Array of optical sensors 48 (or arrangement of pneumatic proximity sensors 49)
Using this method, it is possible to detect more than one wrinkle or curvature on the surface of the recording medium, as well as other factors that affect droplet ejection distance as described above.

For a general discussion of pneumatic proximity sensors 49, see F.J.
Kay, U.S. Pat. No. 3,844,161 and B, A.

Sentyakov et al., “Classification of Pneumatic Proximity Position Sensors,” Machine and Tooling,
Vol. 48, ml, pp. 36-3, 1977. This type of pneumatic device basically consists of a transmitter that directs one or more jets of compressed air toward the object to be detected; A receiver that responds to changes in air pressure caused by changes in distance from the target to the receiver.
Typically, pneumatic transmitters and receivers are formed as a single unit and are extremely accurate over distances from 0.5 to 21 meters from the sensing target, with sensitivity tolerances of up to about 10 microns.

As mentioned above, drop distance sensor 34 is mounted on support member 51, which may be fixed or translatably movable. Any known means (not shown) may be used to translate the support member between at least two positions in the direction of arrow 53 - by way of example, the means may be moved in one direction of translation. The support member may be biased and moved along the other direction by a solenoid or a cam acting on a follower integral with the support member.

In summary, the present invention monitors changes in the distance from the nozzle to the recording medium surface, called the droplet ejection distance or depth of focus, and adjusts the charging electrode voltage or the deflection electrode voltage to compensate for increases or decreases in the droplet ejection distance. The present invention is concerned with improving drop placement accuracy in a multi-nozzle continuous flow pagewidth inkjet printer. The droplet ejection distance is determined by an array of electro-optic sensors each having a light emitter such as an LED and a photodiode receiver for receiving reflected light, or by a compressed gas source such as air directed from an aperture to the recording medium, and an aperture. It is monitored by an array of pneumatic proximity sensors having differential pressure monitoring means for detecting changes in the ratio of the pressure at the bore and the pressure of the pneumatic source. The drop distance sensor can monitor selected areas of the recording medium from either a fixed support member or a translatable support member. The support member and the sensor are positioned below the trajectory of the ink drop and spaced from the surface of the recording medium by a distance of 0.5 to 4 mils for optical sensors and 0.5 to 2 mils for pneumatic proximity sensors. Ru. By translating the support member of the sensor, it is possible to detect the droplet ejection distance for at least twice as many areas on the recording medium as would be detected with a fixed sensor support member.

Embodiments and modifications of the present invention other than those described above will become apparent to those skilled in the art from the specification and drawings, and such embodiments and modifications other than those described above are also included within the scope of the present invention. .

[Brief explanation of drawings]

FIG. 1 is a schematic elevational view of a multi-nozzle continuous flow pagewidth ink jet printer incorporating a distance sensing device used to correct ink drop trajectories that cause variations in drop distance. Figure 2 is a plan view of a part of the blink shown in Figure 1, showing the change in distance from the surface of the recording medium to the printer nozzle in the direction across the width of the recording medium, that is, the change in droplet ejection distance between the nozzles. For illustration purposes, it is a diagram showing a distance sensing device, a printing standard surface, and a recording medium (dotted lines). DESCRIPTION OF SYMBOLS 10... Inkjet printer, 12... Inkjet generator, 14... Ink flow, 15... Nozzle 19... Printing surface, 20... Recording medium, 24...
・Ink droplet (charged droplet), 26...Charged electrode, 27...
・Comparison and comparison signal generation means (control means), 28...
Polarizing electrode, 29...Drop IvL path, 30...Drain groove, 3
1... Second drain groove, 32... Calibration sensor, 34.4
8゜49... distance detection sensor (48... electro-optical device, 49... pneumatic proximity detection sensor), 38...
Controller, 42.52...Drop trajectory adjustment means, 51
...Supporting member. Input FIG, /

Claims (1)

Claims: 1. A grounded, pressurized ink drop generator having a linear array of nozzles that fire streams of ink directed toward a moving recording medium, and an ink drop generator for each stream of ink. a charging electrode positioned at a location where the ink drop is formed and where each ink drop is encoded with a voltage representing the digitized information; a deflection electrode that directs passing ink droplets to a specific position on a recording medium or a drainage groove in response to a voltage; a calibration sensor that calibrates the ink droplets so that the ink droplets are accurately sewn together on a predetermined printing surface; In a continuous flow inkjet printer having a controller for operating the printer: a linear array of distance sensing sensors mounted on a support member located below the ink droplet trajectory, the distance sensing sensors being parallel to the surface of the recording medium; and perpendicular to the direction of movement of the recording medium, each distance sensing sensor producing a signal representing the actual droplet distance from one or more nozzles to the surface of the recording medium at a predetermined period of time; means for comparing said signal representing the droplet distance with a signal representing a predetermined droplet distance; means for generating a comparison signal in response to a comparison of both the actual and predetermined droplet distance signals; and adjusting ink drop trajectories in response to said comparison signal to correct ink drop trajectories for changes in drop distance for a given printed surface; means for maintaining ink drop placement accuracy despite changes in the ink jet printer. 2. The distance detection sensor is an electro-optical device having a light emitter that directs light toward the surface of the recording medium and a light receiver that receives light reflected from the surface of the recording medium, and the electro-optical device is a light receiving and reflecting device. An inkjet printer according to claim 1, which generates a signal representing an actual droplet ejection distance based on light. 3. Pneumatic proximity, wherein the distance sensing sensor has an aperture that directs the compressed gas source towards the surface of the recording medium and pressure monitoring means that detects the difference between the pressure at the aperture and the pressure of the compressed gas source. 2. The inkjet printer of claim 1, wherein the pneumatic proximity sensor generates a signal indicative of the actual drop distance based on changes in the pressure difference sensed by the pressure monitoring means. 4. The inkjet printer according to claim 1, wherein the distance detection sensor is a combination of an electro-optical device and a pneumatic proximity sensor. 5. The controller of the printer, in response to receiving the comparison signal, based on extrapolation between the two or more comparison signals, to a pixel on the recording medium located between the areas of the recording medium actually detected by the distance sensing sensor. An inkjet printer according to claim 1, wherein the trajectory of the directed ink droplets is adjusted. 6. The support member having the array of distance detection sensors is translated back and forth by a predetermined distance along a direction parallel to a predetermined printing surface and perpendicular to the moving direction of the recording medium, so that each distance detection sensor is moved. An inkjet printer according to claim 1, further comprising means for detecting the position of more than one surface area along the linear width of the recording medium.